The present invention relates to a simple structure of sputtering target/backing plate capable of sufficiently accommodating further high-power sputtering without deteriorating the characteristics of a copper-zinc alloy backing plate that is inexpensive and excels in strength and anti-eddy current characteristics.
In recent years, copper alloy with favorable thermal conductivity is generally used as the cooling/support substrate of a sputtering target. For instance, Patent Document 1 describes that brass, aluminum bronze and work-strengthened pure copper do not get scratched easily and possess sufficient strength and thermal conductivity in comparison to the conventionally used pure copper (oxygen-free copper), aluminum (aluminum alloy) and stainless steel.
Moreover, Patent Document 2 describes copper alloy containing 0.5 to 2 wt % of chromium, in particular JIS Z3234 (containing 1 wt % of chromium) as a representative example of the material of a chromium-copper backing plate.
In addition, Patent Document 3 describes that a copper alloy or an aluminum alloy backing plate having a specific resistance value of 3.0 μΩ·cm or greater and tensile strength of 150 MPa or greater is effective for reducing, as much as possible, the eddy current that arises from the rotation of the magnet during magnetron sputtering and inhibiting the variation in the rotation speed of the magnet, and thereby inhibiting the variation in the effective flux, improving the uniformity of the film, increasing the deposition speed, and improving the productivity.
The Examples of Patent Document 3 describe diffusion bonding of a high-purity Cu target (6N) and brass having a specific resistance of 7.2 μΩ·cm and tensile strength of 320 MPa to prepare a sputtering target-backing plate assembly with a total thickness of 17 mm.
Patent Document 4 describes that it is effective to insert an aluminum or aluminum alloy plate having a thickness of 0.5 mm or greater in a tantalum or tungsten target-copper alloy backing plate assembly with minimal deformation after the diffusion bonding, without debonding or cracks between the target and backing plate, and capable of withstanding high-power sputtering. In the Examples, copper-chromium alloy and copper-zinc alloy are used for the copper alloy backing plate.
Patent Document 5 describes a copper or copper alloy target/copper alloy backing plate capable of favorably balancing the anti-eddy current characteristics in the copper or copper alloy sputtering target and the characteristics required in the other magnetron sputtering targets. Patent Document 5 additionally describes that a low-beryllium copper alloy or Cu—Ni—Si based copper alloy backing plate is suitable for the copper alloy backing plate, and further requires a conductivity of 35 to 60% (IACS), and a 0.2% yield strength of 400 to 850 MPa.
Moreover, as a method of resolving problems caused by the heat generated from the target, proposed is a target/backing plate assembly in which a target and a backing plate with higher thermal conductivity than the target are integrated directly, or by the explosive bonding method, hot rolling method and the like via a spacer having a higher melting point than the target (refer to Patent Document 6).
In the case of the Al alloy target, pure silver, titanium, nickel and the like are listed as the spacer. Patent Document 6 describes that it is possible to speed up the deposition and increase the temperature of the target, and therefore possible to stably form high-quality thin films.
Moreover, Patent Document 7 describes that it effectuates the cooling efficiency of the target by inserting copper or aluminum or the alloy thereof between the target and the backing plate (backing plate material is Cu, Al, Cu93-Al17, or Cu4-Al96).
Here, Patent Document 7 describes that this is effective against such problems caused by uneven cooling as structural change due to the recrystallization of the target material, deformation (warping) due to the thermal stress of the target material, deterioration in the sputtering efficiency, and meltdown of the target. It is described that, preferably, the insert is of an area that is 70% of the target or greater and the thickness is roughly 0.05 to 0.5 mm.
In addition, Patent Document 8 describes a sputtering device characterized in that a reaction preventer for preventing the reaction between the target and the backing plate is provided at least on the front face of the backing plate right under the erosion or on the back face of the target. Patent Document 8 further describes that the reaction preventer should be high-melting-point metals or any their nitrides, silicides, carbides or borides, or the graphite layer embedded in the groove, or a hollow.
Patent Document 8 describes that it is possible to prevent situations where the target cannot be removed from the backing plate due to the reaction with the heat from sputtering when replacing the target, and where the contamination results from diffusion of copper consisted in the backing plate into the target and intrusion thereof into the formed thin film as impurities.    [Patent Document 1] Japanese Patent Laid-Open Publication No. H1-222047    [Patent Document 2] Japanese Patent Laid-Open Publication No. H8-269704    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-329362    [Patent Document 4] Japanese Patent Laid-Open Publication No. 2002-129316    [Patent Document 5] WO2005/064036    [Patent Document 6] Japanese Patent Laid-Open Publication No. H4-131374    [Patent Document 7] Japanese Patent Laid-Open Publication No. H11-189870    [Patent Document 8] Japanese Patent Laid-Open Publication No. S63-45368
The foregoing background art was obtained from patent gazettes, but as recent technology the linearity of sputtered particles to be deposed on the wafer is controlled by increasing the sputtering power and improving the ionization efficiency of the sputtered particles in order to form a fine wiring network of 90 nm to 65 nm process or the like.
For example, this kind of sputtering process is referred to as the self ionized process. Depending on the status of the magnetic field that arises due to the magnetron rotating at the rear of the backing plate in the sputtering device, there are cases where the heat generated in the severely eroded area of the target becomes extremely high.
Generally speaking, copper-zinc alloy is used as the backing plate material, since it can be manufactured inexpensively, has high strength and superior thermal conductivity, and is able to inhibit the generation of the eddy current. Nevertheless, even when this kind of effective copper-zinc alloy is used for the backing plate, an additional problem has arisen in that zinc, an additive alloy element, evaporates at the portion where the erosion is concentrated and debonding occurs at the diffusion bonded interface.
In particular, this kind of problem has frequently occurred with a tantalum or tantalum-based alloy target having low thermal conductivity. Since the heat dissipation lines were cut off at the portion debonded from the backing plate, when sputtering was continued while neglecting this status, the target was partially melted down due to the heat accumulation and there were cases that sputtering could not be continued.
With the other targets (for instance, copper-0.5% aluminum alloy target), since the thermal conductivity of the target itself is significantly higher than the thermal conductivity of tantalum, a meltdown would not occur. Nevertheless, trace amounts of zinc were detected in the sputtering atmosphere.
The reason why zinc transpires is because the vapor pressure is high, and even from hypothetical numerical calculation results, it has been discovered that problems arise when the highest temperature of the backing plate at the bonded interface right under the most eroded position exceeds roughly 500° C.